Whether you’re behind the wheel of a classic muscle car or a loveable old pickup, there’s a good chance it’s riding on a set of drum brakes. These tried-and-true stoppers have been slowing things down, using simple mechanics and cheap-to-manufacture parts, for more than a century.
How do drums, then, come to dissipate kinetic energy as heat to slow down your ride? We’ll take you through the inner workings of that old technology, which, believe it or not, is often better at actually stopping your vehicle than discs.
Drum Brake System Components
Brake Drum and Wheel Cylinder
When you’re relying on drum brakes, the brake drum and wheel cylinder are working hard.
Your vehicle’s brake drum is bolted to your wheel hubmaking it pointlessly difficult to stop spinning with the wheel. Your wheel cylinder converts hydraulic pressure to mechanical force, pushing those brake shoes against the wheel drum, and getting the job done.
Brake Shoes and Springs
The drum makes the shoes turn! You rely upon the brake shoes to throw up friction. There are two types, the primary and the secondary.
What’s the difference between brake pads and brake shoes? The pads are used on disc brake systems.
Springs hold them there and throw them back after your brakes are off.
Back Plate and Adjuster
Your backing plate just serves as a solid foundation for housing the individual parts, plus protecting all that from debris. It absorbs the torque of braking action, and so is sometimes known as the “Torque Plate.”
Together with the plate, the adjuster fits them as far apart as they should be. This is of prime importance if you want your brakes to work properly.
How Drum Brakes Work
Let’s take a look inside the drum brakes on your car. You step on the brake pedal and pressurize the hydraulic brake fluid, which moves through the brake lines and does what must be done to slow and stop your vehicle.
The hydraulic pressure acts on a piston in a wheel cylinder, which presses the brake shoes up against the rotating drum itself; it is primarily the friction between the shoes and drum that brings your car to a fast stop.
Older vehicles (up to the early 1970s) used drum brakes all round, then rear drum brakes were common portals, and disc brakes are now generally fitted to front wheels. Almost all modern vehicles have discs all round, but there are still some cars with drum brakes fitted to the rear.
Heat and Friction
When you press down on your brake pedal, you might not realize how much heat and friction are involved in stopping your car. Drum brakes in particular require those forces to help bring your vehicle to a halt.
Friction occurs when the brake shoe comes into contact with the rotating drum brake. The brake shoe is made with specific materials that create the right amount of friction to slow your vehicle without damaging itself or other components. As the drum turns and hits the brake shoe, friction builds up and slows the wheel.
Heat is also generated as the drum rubs against the brake shoe and a great deal of heat occurs as a result of that friction. The brake drums are traditionally made of cast iron, which is very resistant to heat and wear.
That makes it unlikely that the drum won’t lose its shape, even when the temperature rises in braking. Interestingly, a great deal of the friction material used in drum brakes has an effect on the overall system! Like brake pads, certain materials accelerate the dissipation of heat and lower stopping distances!
Drum Brake Maintenance and Repair
Regular Checks and Cleaning
To keep your drum brake system in tip-top shape, regular checks and cleaning are essential. Start by checking out the brake shoes for wear – check for signs of damage, including uneven wear, which wouldn’t be helpful for braking.
Of course, the brake drums and other bits should also be kept clean. You may want to remove the wheel, plus the drum. When you do this, use some brake cleaner to blast away this dirt and grime.
Give parts that need lubricating a squirt too, like the adjuster or areas where the shoes touch the backing plates.
Replacement
After lots of use, wear on brake shoes, springs, and the rest can make drum brake systems less efficient. You may want to consider replacing your system if experiencing the following:
- The braking feels spongy or very soft at the pedal.
- A car pulls to one side when braking at all.
- Grinding or squeaking sounds while braking.
Advantages and Disadvantages of Drum Brakes
Pros
- Longer lifespan thanks to a larger area of inclusion that makes contact.
- More stopping power than an equal diameter disc brake.
- Cheaper to produce.
- Easier and cheaper to maintain because everything is enclosed in one component.
- Needs less maintenance because of better corrosion resistance.
Cons
- More difficult to use when compared to disc brakes.
- Needs a special brake tool that helps meek springs to spring loose when you want to replace parts.
- Disperses lower heat, which could be a hazard in cold regions.
- Usually confined to the back wheels, and hence overall vehicle attitude is impaired when compared against disc brakes on front wheels.